GB2109276A

GB2109276A - Method for the manufacture of prefabricated components from high-alloy ferritic materials and components made by the method

Info

Publication number: GB2109276A
Application number: GB08226460A
Authority: GB
Inventors: Hans-Josef Laudenberg; Richard Weintz
Original assignee: Teves Thompson and Co GmbH
Current assignee: Teves Thompson and Co GmbH
Priority date: 1981-09-16
Filing date: 1982-09-16
Publication date: 1983-06-02
Also published as: ES8306186A1; PT75560B; JPH027366B2; GB2109276B; DE3136722C2; JPS5861227A; ES515717A0; FR2512834A1; DE3136722A1; FR2512834B1; IT1210934B; IT8223280A0; PT75560A

Abstract

Prefabricated components are made from a high-alloy ferritic material by heating the alloy to a temperature of about 1,100 DEG C at which it becomes austenitic, cooling the alloy to a temperature between 200 DEG C and 500 DEG C at which it is still austenitic and forming it by a compression or extrusion technique.

Description

SPECIFICATION Method for the manufacture of prefabricated components from high-alloy ferritic materials and components made by the method This invention concerns a method for the manufacture of prefabricated components, particularly internal-combustion-engine valves, from high-alloy ferritic materials by means of a non-cutting, forming process, and components made by the method.

It is known that prefabricated components such as valves for internal combustion engines can be manufactured from low-alloy steel by cold compression and cold extrusion in several stages and with special cold-moulding machines, called "cold-headers". A prerequisite for compression and cold extrusion is the low tensile strength and high elongation values of the low-alloy materials, which allow good, flawless forming to be achieved.

Valves made from high-alloy materials, which can be ferritic, martensitic or austenitic, could not, until now, be manufactured by such cold-moulding machines since the shaping force required was too high, the deforming property of the material too poor and there was too great a danger of flaw formation.

Prefabricated components which have been made up to now from such materials have therefore been manufactured by means of hot-extrusion or by electric resistance heating with simultaneous compression and impaction in the die. The shaping takes place at a temperature of between 950"C and 1200"C. The deforming properties are then at their best and the danger of flaw-formation slight.

Manufacturing by cold forming has technical production advantages. It gives a high production rate per unit time coupled with a high precision finish and also a long tool life. The production is thus economically favourable. The disadvantage, however, lies in the fact that higher-alloy materials cannot be formed entirely under cold conditions to the desired extent since they have too great a resistance to deformation and a flaw susceptability. It is of some help to warm the high-alloy materials to a forging temperature. After warming the high-alloy material can be formed into prefabricated components by hot extrusion and compression.

This method is however, much less economical because of the lower output per unit time approximately 15 pieces per minute from hot extrusion and approximately 30 pieces per minute from a modern compression device, compared with 60 pieces per minute from a pure cold-moulding process. Furthermore the precision finish is poorer.

In order to reduce the resistance to deformation it is also known to pre-heat the material to a temperature of between 200"C and 500"C or even to a higher temperature in some cases so that semi-hot forming can then be carried out. The advantages of cold-forming as regards the precision finish are hereby maintained.

Experiments with high-alloy materials, such as are used in the manufacture of valves for internal combustion engines, have shown, however, that the resistance to deformation is only slightly reduced and that the elongation values cannot be improved so as to avoid flaw formation during the forming.

The object of this invention is to make it possible to use high-alloy ferritic material for the manufacture of prefabricated components under semi-hot conditions with the aid of known shaping machines with all their advantages. Accordingly the present invention provides a method for manufacturing prefabricated components from high-alloy ferritic materials by means of a forming process including the following steps: (a) austenitizing the high-alloy, ferritic starting material; (b) cooling the austenitized material to a temperature within a range in which the austenite is still stable; (c) forming the austenitic material into the finished component at the temperature to which it has been cooled.

It is found that the material is stable in the austeniticform over a long period of time in a temperature range between the formation of perlite and martensite and therefore no conversion takes place so that forming is possible: owing to the established slow conversion above the martensite conversion temperature of high-alloy ferritic martensitic steel there is sufficient time to cool the material and to form it into the prefabricated components according to the technical process. In particular, in the austeniticform, compared with the ferritic form, the material requires a smallerforming force, and has an increased elongation value so as to avoid flaw formation during the forming and allow cold or semi-hot forming processes to be employed with their advantages of precision finishing and the high rate of production of the components per unit time.

The austenitic material can thus be formed into components such as valves on "cold-headers" without any difficulty.

The starting, ferritic material is preferably heated to a temperature of approximately 1,1 00 C in order to austenitize it and is then cooled in step (b) to a temperature within the range substantially 200"C to 500"C.

According to a further aspect, the invention also provides a prefabricated component manufactured by the method outlined above and comprising the following elements in the proportions given below in percentages by weight: Element Range of % by weight C 0.20- 1.00 Si 0.50 - 4.00 Mn 0.50 - 3.00 P 0 - 0.045 S 0 - 0.030 Cr 4.00 - 20.00 Mo 0 - 4.00 Ni 0 - 2.00 V 0 - 2.00 W 0 - 2.00 Fe rest More preferred proportions for the components are: Element Range of % by weight C 0.40 - 0.50 Si 2.70 - 3.30 Mn 0 - 0.8 P 0 - 0.040 S 0 - 0.030 Cr 8.0 - 10.0 Ni 0 - 0.5 Fe rest Several examples of compositions for making high-alloy components according to the present invention are given below:: TABLE 1 % by weight Element Example Example Example Example Example 1 2 3 4 5 C 0.40 0.08 0.85 0.45 0.46 Si 2.50 2.00 1.00 max 3.00 1.00 max Mn 0.8 max 1.00 max 1.50 max 0.80 max 1.00 max P 0.04 max 0 0.04 max 0.04 max 0.045 max S 0.03 max 0 0.03 max 0.03 max 0.030 max Cr 10.00 14.75 17.50 9.00 13.50 Mo 1.05 1.00 2.25 0 0 Ni 0 0.75 0 0.50 max 0 V 0 0 0.45 0 0 W 0 1.00 0 0 0 Fe Rest Rest Rest Rest Rest Experiments with the above high-alloy steel starting materials have shown that, after heating to the austenitic temperature of approximately 1,100"C and cooling to 200"C-500"C, the treated material can then be formed by the usual cold-compression and cold extrusion techniques in cold-moulding machines.

The advantages of the method according to this invention can clearly be seen from Table 2 below which gives the average values of results obtained from tests carried out on three sets of samples, a), b) and c), made by different methods: a) the samples were obtained at room temperature; (the initial state is given as 100%) b) the samples were obtained after pre-heating of the starting material to 4000C; c) the samples were obtained from material austenitized according to this invention, and cooled to 400"C.

In Table 2 below, ReH indicates the elastic limit stress, RM indicates the tensile strength, A indicates the percentage elongation at fracture and Z indicates the percentage contraction at fracture, according to DIN 50 145.

TABLE 2 Samples ReH RM A Z N/mm2 N/mm2 % a) 596(100%) 823(100%) 23.9 (100%) 52 (100%) b) 390( 65%) 570( 69%) 26.0(109%) 58(112%) c) 225 ( 38%) 586 ( 71%) 64.4 (269%) 69(133%) This clearly shows a reduction in the tensile strength and a considerable increase in the elongation of those samples which were treated in accordance with this invention.

The exact composition of the ferritic material used for the test samples a), b) and c) was as follows: Element % by weight C 0.46 Si 3.00 Mn 0.35 S 0.003 P 0.0021 Ni 0.10 Cr 9.13 Fe

Claims

1. A method for the manufacture of prefabricated components from high-alloy ferritic materials by means of a forming process including the following steps: a) austenitizing the high-alloy, ferritic starting material; b) cooling the austenitized material to a temperature within a range in which the austenite is still stable; c) forming the austenitic material into the finished component at the temperature to which it has been cooled.

2. Method as claimed in Claim 1, in which the starting material is heated to approximately 1,100"C to austenitize it.

3. A method as claimed in Claim 1 or Claim 2, in which the temperature range of step b) is substantially 200"C-500"C.

4. A method as claimed in any one of Claims 1-3, in which the forming is achieved by compression.

5. Method as claimed in any one of Claims 1-4, in which the forming is achieved by extrusion.

6. A prefabricated component manufacture by the method of any one of Claims 1-5, and comprising the following elements in the proportions given below in percentages by weight: Element Range of % by weight C 0.20- 1.00 Si 0.50- 4.00 Mn 0.50 - 3.00 P 0 - 0.045 S 0 - 0.030 Cr 4.00 - 20.00 Mo 0 - 4.00 Ni 0 - 2.00 V 0 - 2.00 W 0 - 2.00 Fe rest

7. A prefabricated component as claimed in Claim 6, in which the elements are present in the following percentages by weight: Element Range of % by weight C 0.40 - 0.50 Si 2.70 - 3.30 Mn 0 - 0.8 P 0 - 0.040 S 0 - 0.030 Cr

8.0 - 10.0 Ni 0 - 0.5 Fe rest